A known personal vehicle, for example, a wheelchair includes a vehicle body having a seating portion on which a user is to be seated, a right-hand side wheel provided at the vehicle body and positioned at a right-hand side of the user seated on the seating portion, and a left-hand side wheel provided at the vehicle body and positioned at a left-hand side of the user seated on the seating portion. An operation portion to which a command value related to a vehicle body travel speed and a vehicle body turning angle is inputted is provided at the vehicle body of the personal vehicle.
A drawback is involved in a case where a roll angle relative to a roll axis of the vehicle body is assumed to be large because an inclination of a road surface has a steep angle when the personal vehicle travels straight in a direction to transverse on an inclined road surface (i.e., hereinafter referred to as cant travel). That is, despite the operation of the operation portion by the user to move the vehicle straight, a moving direction of the vehicle body may be unintentionally changed to a downward direction due to gravity on the road surface to deteriorate a straight traveling performance of the personal vehicle.
JP2010-193939A (hereinafter referred to as Patent reference 1) discloses a personal vehicle control device which reduces the foregoing drawback. The personal vehicle control device disclosed in Patent reference 1 includes a control portion for executing a control (here, the control is referred to as a fourth control law for an explanatory purpose) for ensuring a straight traveling performance of the personal vehicle by restraining an unintentional change in a moving direction of the vehicle body to a downward direction due to gravity as long as the operation portion is operated to move the personal vehicle straight even if the roll angle of the personal vehicle is large when the personal vehicle performs the cant travel.
FIG. 11 shows a flowchart of the fourth control law disclosed in Patent reference 1. The fourth control law is executed in the following manner. First, the control portion reads-in the roll angle of the vehicle body (inclination angle of the road surface) (Step S402). In a case where the roll angle of the vehicle body (inclination angle of the road surface) is equal to or greater than a predetermined level (i.e., YES at Step S404), the control portion obtains a turning angular velocity ωgyaw of the personal vehicle relative to a yaw axis detected by a rate gyro provided at the personal vehicle (Step S406). Next, the control portion obtains a turning angular velocity command value ωref inputted from the operation portion (Step S408). Further, the control portion obtains a difference of the turning angular velocity command value ωref from the turning angular velocity ωgyaw or a ratio of the turning angular velocity command value ωref relative to the turning angular velocity ωgyaw (Step S410).
Further, in a case where the difference of the turning angular velocity command value ωref from the turning angular velocity ωgyaw or the ratio of the turning angular velocity command value ωref relative to the turning angular velocity ωgyaw is equal to or greater than a predetermined level (i.e., YES at Step S412), the control portion multiplies a turning angular velocity feedback gain to the difference of the turning angular velocity command value ωref from the turning angular velocity ωgyaw or to the ratio of the turning angular velocity command value ωref relative to the turning angular velocity ωgyaw to obtain a rotation angular velocity correction value of wheels at the right-hand side and the left-hand side. Based on the rotation angular velocity correction value, a rotation angular velocity command value {dot over (θ)}R—ref of the right-hand side wheel that the user commanded is corrected, and a rotation angular velocity command value {dot over (θ)}L—ref the left-hand side wheel that the user commanded is corrected (Step S414).
Further, the control portion corrects a drive torque TR of the right-hand side wheel on the basis of a difference between a rotation angular velocity {dot over (θ)}R of the right-hand side wheel detected by a right-hand side wheel encoder and the rotation angular velocity command value {dot over (θ)}R—ref of the right-hand side wheel, and on the basis of a difference between a rotation angle θR of the right-hand side wheel detected by the right-hand side wheel encoder and an integral value of the rotation angular velocity command value {dot over (θ)}R—ref. Further, the control portion corrects a drive torque TL of the left-hand side wheel on the basis of a difference between a rotation angular velocity {dot over (θ)}L of the left-hand side wheel detected by a left-hand side wheel encoder and the rotation angular velocity command value {dot over (θ)}L—ref of the left-hand side wheel, and on the basis of a difference between a rotation angle θL of the left-hand side wheel detected by the left-hand side wheel encoder and an integral value of the rotation angular velocity command value {dot over (θ)}L—ref (Step S416). Accordingly, an unintentional change in a moving direction of the vehicle body of the personal vehicle, which is in cant travel, to a downward direction due to gravity is restrained.
According to the fourth control law of Patent reference 1, the rotation angular velocity correction value of the wheels at the right-hand side and left-hand side is obtained only based on the difference of the turning angular velocity command value from the actually measured turning angular velocity of the personal vehicle or the ratio of the turning angular velocity command value relative to the actually measured turning angular velocity. Accordingly, by repeatedly executing the fourth control law, the difference between the turning angular velocity command value and the actually measured turning angular velocity gradually approaches to zero (0), or the ratio of the turning angular velocity command value relative to the actually measured turning angular velocity gradually approaches to one (1), so that the unintentional change in a moving direction of the vehicle body of the personal vehicle to a downward direction due to gravity is gradually restrained. However, the fourth control law according to Patent reference 1 cannot sufficiently correct the unintentional change in a moving direction of the vehicle body to a downward direction due to gravity and a deviation of the turning angle that are once generated at the personal vehicle. Accordingly, in a case where the cant travel continues for a long period of time, the unintentional change in a moving direction of the vehicle body to a downward direction due to gravity of the personal vehicle and deviation of the turning angle are accumulated to deteriorate the straight traveling performance of the personal vehicle.
In the cant travel of the personal vehicle, when starting the cant travel, the unintentional change in a moving direction of the vehicle body of the personal vehicle to a downward direction due to gravity and the deviation of the turning angle are likely to occur. In those circumstances, as explained above, with the fourth control law according to Patent reference 1, once the unintentional change in a moving direction of the vehicle body to a downward direction due to gravity occurs and the deviation of the turning angle are generated because the correction is not sufficient, the unintentional change in a moving direction of the vehicle body to a downward direction due to gravity and the deviation are not corrected, that is, a state cannot be returned to the original state. Further, according to the control of the fourth control law which uses a feedback correction, a time is required to correct the generated unintentional change in a moving direction of the vehicle body to a downward direction due to gravity and to correct the generated deviation of the turning angle to return to the original state.
A need thus exists for a synchronous motor control device which is not susceptible to the drawback mentioned above.